The goal of this Mentored Career Development Award is to facilitate Dr. George Kyei's transition to independence as a physician-scientist studying how the human immunodeficiency virus (HIV) is able to survive in latently infected cell like resting T cells and macrophages. The proposed experiments will be conducted under the mentorship of Dr. Lee Ratner, and they will examine the role of the protein cyclin L2 and how it controls HIV replication in the aforementioned cell types. HIV continues to be a global pandemic with over 35 million people living with the virus. In the United States, over 50,000 new infections happen every year. Although current anti-retroviral therapy (ART) can suppress the virus and improve the quality of life for patients, these treatments do not lead to cure. Within weeks of patients stopping therapy, the viral load begins to rise again. Lifelong treatment has the attendant problems of patient fatigue, drug side effects and unsustainable costs. Hence viral elimination or cure is a vital goal. The main reason for viral resurgence upon treatment interruption is the presence of viral reservoirs like resting T cell and macrophages, which have the virus integrated in their genomes in a resting state. As soon as treatment is interrupted, these cells serve as sources of virus. Despite their crucial role in sustaining HIV persistence, current knowledge of viral replication requirements in macrophages and resting T cells is very limited. Recently, we identified cyclin L2 as critical for HIV replication in macrophages. The goal of this project is to test the hypothesis that cyclin L2 controls HIV replication in macrophages and resting T cells by modulating viral alternative splicing in cooperation with specific cellular kinases. In order to test this hypothesis, we will use biochemical, molecular genetics, genomics and proteomics approaches to test the following specific aims: 1. to characterize the mechanisms by which cyclin L2 controls HIV pre-mRNA alternative splicing. We will use gene knockdown, polymerase chain reaction, whole genome RNA sequencing and biochemical methods to define how cyclin L2 controls the splicing of HIV. 2. To determine the effect of phosphorylation on cyclin L2 function. Cyclin L2 is known to be heavily phosphorylated. We will use proteomics, gene knockdown approaches and specific kinase inhibitors to investigate the importance of Dyrk1A and CDK11B as potential kinases for cyclin L2. 3. To identify and characterize the molecular domains of cyclin L2 required supporting HIV replication in non- cycling cells. The rationale for this aim is to identify the exact motifs of cyclin L2 required forHIV replication, in order to map out a potential therapeutic target. . The proposed experiments will shed new light in our understanding of HIV replication requirements in these critical cell types and potentially reveal novel molecular targets for HIV elimination.